1. Field of the Invention
This invention relates generally to a sound image processing system for positioning audio signals reproduced over headphones and, more particularly, for causing the apparent sound source location to move relative to the listener with smooth transitions during the sound movement operation.
2. Description of Background
Due to the proliferation of sound sources now being reproduced over headphones, the need has arisen to provide a system whereby a more natural sound can be produced and, moreover, where it is possible to cause the apparent sound source location to move as perceived by the headphone wearer. For example, video games both based on the home personal computer and based on the arcade-type games generally involve video movement with an accompanying sound program in which the apparent sound source also moves. Nevertheless, as presently configured, most systems provide only a minimal amount of sound movement that can be perceived by the headphone wearer and, typically, the headphone wearer is left with the uncomfortable result that the sound source appears to be residing somewhere inside the wearer's head.
A system for providing sound placement during playback over headphones is described in U.S. Pat. No. 5,371,799 issued Dec. 6, 1994 and assigned to the assignee of this application. In that patent, a system is described in which front and back sound location filters are employed and an electrical system is provided that permits panning from left to right through 180.degree. using the front filter and then from right to left through 180.degree. using the rear filter. Scalers are provided at the filter inputs and/or outputs that adjust the range and location of the apparent sound source. This patented system requires a large number of circuit components and filtering power in order to provide the realistic sound image placement and in order to permit movement of the apparent sound source location using the front and back filters, a pair of which are required for the left and right ears.
At present there exists a need for a sound positioning system for use with headphones that can create three-dimensional audio imaging without requiring complex and expensive filtering systems, and which can permit panning of the apparent sound location for one or more channels or voices.